Cities are using walls of moss to tackle air pollution from traffic

Walls covered in moss are popping up in major cities, along with promises that they can help reduce air pollution – but can a few square metres of plant matter really tackle the smog?

Berlin-based firm Green City Solutions believes so. Its moss walls, called CityTrees, are roughly 4 square metres in size. It says they can filter up to 80 per cent of pollution particles out of the air, including the tiny ones linked to respiratory and cardiovascular diseases.

The walls collect rainwater, which is pumped through an irrigation system to …